PARALLEL LINES AND ANGLES

Angles at a point

The sum of the sizes of the angles at a point is 360°.

Two angles which have same vertex and share a common arm are called adjacent angles

∠PAQ and ∠QAR are adjacent angles.

Vertically opposite angles are equal in size.

When two lines are parallel lines are cut by a third line, the angles in corresponding positions are equal in size.

When two parallel lines are cut by a third line, then angles in alternate positions are equal in size.

When two parallel lines are cut by a third line, co-interior angles are supplementary.

Co-interior are also called as consecutive interior angles.

Two angles are complementary, if the sum of their measures is equal to 90.

Two angles are supplementary angles if the sum of their measures is equal to 180 degrees.